How to think about… Alien contact

“We must realise that there are other worlds in other parts of the universe, with races of different men and different animals.” That was the Roman poet Lucretius, writing in the 1st century BC.

Only in the past few decades have we grasped the truth of the first part of that statement, thanks to planet-hunters such as NASA’s Kepler space telescope. Almost 5000 suspected planets have already been spotted outside our solar system, and stars nursing planets seem to be the rule, not the exception. With hundreds of billions of stars in our galaxy alone, that’s an awful lot of worlds.

Surely, then, it’s only a matter of time before we confirm the second part by finding signs of life.

This is the central dilemma of searches for ET, says Jeffrey Scargle of the NASA Ames Research Centre in Moffett Field, California. “You can’t assume nothing because then you don’t even know how to start looking, but if you assume too much then you’re biased and you’re not open to finding a lot of things that might be there.”